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daddymikey1975 01-22-2012 07:23 AM

insulating the attic in my cape cod question
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I have a cape cod and my attic space needs some insulation (there really isn't any) and I'm considering blowing some insulation up there but there's a caveat.

I 'drew' a picture w/ microsoft paint to help depict my dilemma.. in the 'attic' there is rolled insulation (the red line) on the attic side of the upstairs 'knee' walls. on the floor of the attic they installed 'sub flooring' to use as additional storage space. under the subflooring there is nothing but air, then the drywall from the lower level living space (see the 'box' on the top right side of my picture).

the triangular portion of my attic needs some insulation. there is a ridge vent for the roof (above the upstairs living space) and there are soffit vents where the lower level walls meet the roof line behind the gutters.

What i was considering doing was putting a hole in the attic subfloor near the soffit vent (to allow air to escape while filling the gap) and a hole near the upstairs knee wall (to use as the entry point for the cellulose).. my question is, the joists are only 2x8 so the max thickness of insulation that I can blow in there is 8".. will this be sufficient thickness to be effective ?

Thanks for your help.

nealtw 02-09-2012 12:14 AM

I would cut an access hole thru the wall so when you do this you can be sure not to plug the soffet vents. There would be no problem putting in 12" of insulation. If this area is more than 100 sq.ft. you should have an access door. Or just repair wall when done.

GBR 03-03-2012 03:05 PM

Little different in the States; 30 sq.ft. and 30" headroom:

The moving air you have now is controlling condensation. After insulating and air-sealing, the "first condensing surface" will be the flooring- remove it;

Housewrap the knee wall insulation to prevent wind-washing. Air block under the K.W. Define your air/thermal barriers;


chefman45887 08-15-2012 03:57 PM

with my house even with insulation on floor and knee wall, I installed 1" foilfaced foamboard with 2" roofing capnails and the foamboard caulking and aluminum tape. the heat or cold envelope pending on season is pretty much gone.

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